What investigations are recommended to confirm a diagnosis of Long QT Syndrome in a patient presenting with syncope?

To investigate a patient presenting with syncope where Long QT Syndrome (an inherited cardiac condition) is suspected, the following investigations are recommended:

• Initial Assessment and Referral: A patient with syncope and a family history of sudden cardiac death in people aged younger than 40 years and/or an inherited cardiac condition should be referred for an urgent specialist cardiovascular assessment within 7 days ¹.
• Specialist Cardiovascular Assessment: This assessment involves reassessing the person's detailed history of transient loss of consciousness (TLoC), medical history, and any family history of cardiac disease or an inherited cardiac condition ¹. A clinical examination, including a full cardiovascular examination and, if clinically appropriate, measurement of lying and standing blood pressure, should be conducted ¹. A 12-lead ECG should be repeated, and any previous ECG recordings should be obtained and examined ¹. Based on this assessment, the person is assigned to a suspected cause, such as suspected cardiac arrhythmic or suspected structural heart disease ¹.
• Further Investigations for Suspected Cardiac Arrhythmic Cause:
  • Ambulatory ECG: For people with a suspected cardiac arrhythmic cause of syncope, an ambulatory ECG should be offered ¹. The type of ambulatory ECG (Holter monitoring, external event recorder, or implantable event recorder) is chosen based on the frequency of TLoC ¹. An implantable loop recorder may be considered if there is an inheritable arrhythmia at low risk of sudden cardiac death ³.
  • Exercise Testing: If the syncope occurred during exercise, urgent exercise testing should be offered, unless there is a possible contraindication ¹. Syncope during exercise may also benefit from exercise testing ³.
  • Echocardiogram: An echocardiogram is recommended if structural heart disease is suspected, or if syncope is suspected secondary to a cardiac cause ²,³. This is also indicated if a murmur is found on examination, heart failure is suspected, or the ECG shows signs like left bundle branch block, left ventricular hypertrophy, or Q-waves ².
  • Electrophysiological Study: Further specialist investigations may include an electrophysiological study to assess suspected bradycardia or tachycardia ³.